The present invention relates to a WCDMA (Wideband Code Division Multiple Access) UTRAN (Universal Terrestrial Radio Access Network) system which controls the amount of data on a DCH (Dedicated Channel).
The UTRAN in the WCDMA system is a node which is positioned between a user equipment (UE) such as a mobile terminal and a core network (CN) such as an exchange network and creates an interconnection between them.
FIG. 16 shows a general structure of a UTRAN common to the prior art and the present invention. This figure shows a UTRAN 10 having a schematic structure constituted by base stations 3 and 4 (nodes B) which contain a point Uu as air (radio channel) interfaces to a UE 5 and a base station controller (Radio Network Controller: RNC) 2 which terminates a point Iu as an interface to a CN1.
An RNC contains plural nodes B through an Iub interface, to perform various processings concerning control channels (CCH) for exchanging control data, and traffic channels (TCH) for transferring user data. Of these channels, channels shared among users are called common channels, and channels individually assigned to users are called dedicated channels (DCH).
A representative function of the common channels is the function of paging. A representative function of the dedicated channels is the function of selection-synthesis/distribution to prevent an instantaneous disconnection.
In the UTRAN 10, the DCH on the point Iub as an interface between the RNC and the node B is required to operate according to specifications of Iub Frame Protocol defined in 3 GPP TS25.427 (Technical Specification Group Radio Access Network: UTRAN Iub/Iur Interface User Plane Protocol).
A difference between the uplink OCH (node B→RNC) and the downlink DCH (RNC→node B) is the degree of freedom in selecting normal mode/silent mode. That is, a provider can select the DCH mode in the uplink (UL) side. However, in the downlink (DL) side, the normal mode is indispensable to the node B in the downlink side (Air interface). Therefore, the normal mode must be selected as the mode in the downlink side in the RNC side if one should be selected from two modes of the silent mode and the normal mode.
In the normal mode, the situation of arrivals of valid data is checked for every transmission processing period, and the valid data is transmitted if there is any valid data. Otherwise, if there is no valid data, no-data frames are transmitted. In the silent mode, if there is any valid data, the valid data is transmitted. Otherwise, if there is no valid data, nothing is transmitted.
FIG. 17 shows transmission data in case of adopting the normal mode in the uplink side. If the normal mode is selected in the uplink side, the node B transmits an Iub frame to the RNC within a transmission timing interval (TTI: 10, 20, 40, and 80 ms are defined) for every user regardless whether user data is received from the UE or not.
Data which is transmitted to the RNC when user data is not received is called a no-data frame. The no-data frame does not include the user data but is provided with data concerning radio-quality like the user data.
The RNC can monitor transport-synchronization with the nodes B or the condition of the radio quality at a TTI cycle. Therefore, it is possible to perform fine controls (e.g., recovery from a synchronous error, transmission power control, and the like) in association with the nodes B. However, since frame processing inevitably takes place at the TTI cycle, heavy loads are applied to the bandwidth and the processing capability.
FIG. 18 shows transferred data when the silent mode is adopted in the uplink side. As shown in FIG. 18, when the silent mode is thus adopted in the uplink side, all the data that the RNC receives from the nodes B is user data. The nodes B do not transmit data to the RNC when the user data is not received from the UE.
In this mode, the accuracy deteriorates in the aspects of synchronous errors in transport and monitoring the radio quality, in case of a small data amount. However, if there is no data, cells (data) are not exchanged, and therefore, this mode is more advantageous than the normal mode, from the aspects of the bandwidth and the processing capability. Representative units of the cells described above are ATM (Asynchronous Transfer Mode) packets and IP (Internet Protocol) packets.
FIG. 19 shows transfer of DCH data in the downlink side. For the downlink (RNC→node B) DCH, as shown in FIG. 19, the normal mode is essential. That is, the RNC transmits user data or no-data frames to the nodes B.
Like the uplink side, if there is no valid data, frame assembly and transmission processing are carried out at defined timings in the TTI cycle, in units of users, resulting in heavy loads to the RNC and the nodes B disadvantageously from the aspect of bandwidth.
In the WCDMA system in the current situation, frames are transferred by ATM cells. Therefore, even if there is no data, the bandwidth of 53[oct]/TTI is consumed. For example, in case of TTI=10 [ms], every one user needs at least a bandwidth of 42.4 Kbps (=53[oct]× 8/10 [ms]).
The system thus provides low efficiency if data is transferred in the best effort method of several Kbps. If the system is further multiplied in the future by using existing resources, it may be unavoidable to increase channels due to the problem of the bandwidth.
As described above, the conventional WCDMA UTRAN system exchanges a no-data frame at every TTI between the RNC and the nodes B in the normal mode, even when there is no user data. Heavy loads are applied to the bandwidth and the processing capability.